Simulation of sedimentary dynamics in a small-scale estuary: the role of human activities

Human activities, such as tidal sluice gate construction and reclamation, are prevalent along northern coastline of China and influence significantly sedimentary environments. The Sheyang River estuary is a small estuary situated on the Jiangsu coast. For the objective of storing fresh water, maintaining river channel depth and managing the land resource, a tidal sluice gate was constructed. At the same time, estuarine wetlands have been reclaimed extremely in recent decades. A numerical model based upon Delft3D was developed to quantify the impact of these human activities, and four simulation schemes were designed (a) tidal sluice gate present, but always closed; (b) tidal sluice gate not present; (c) tidal sluice gate present, but closed during flood and open during the ebb; and (d) intertidal area reclamation taking place in the estuary. A bathymetric survey confirmed the erosion and deposition results of the simulation. The rate of sediment deposition increased significantly after the gate was closed. However, during the third scheme, the sediment deposition rate reduced considerably; that was because the ebb current increased the scouring force when the gate was open, especially within the channel area close to the gate. Meanwhile, reclamation lessened erosion behind the gates and may have been enhanced by siltation. The coastline shifted seaward as the siltation area increased; it extended farther because of reclamation. Appropriate coastal management planning strategies must be developed to reduce negative effects of the channel siltation, resulting from the various forms of human activity. The results of this study can provide input to governmental recommendations on more effective tidal gate management strategies.